1. Presented by Kelly Craven, MD, Ph.D. and reviewed by Ming-Tseh Lin, MD, Ph.D. and Lori Sokoll, Ph.D.

Clinical Vignette

An adult initially presented with anemia, a CEA of 450 ng/mL (ref: 0-3 ng/mL) and a CA19-9 of 1500 U/mL (ref: 1-36 U/mL). A colonoscopy showed a mass in the colon. They underwent a colectomy with pathology demonstrating a well-differentiated adenocarcinoma. Family history is significant for colon cancer in first-degree relatives, both of whom presented at an age less than 50 years old. The staining pattern for mismatch repair proteins is below:



The results of the microsatellite instability test looking at 5 different microsatellite markers (NR 21, BAT 26, BAT 25, NR 24, and MONO 27) are below:



Question:
How should these test results be interpreted?